1. Field of the Invention
The present invention relates generally to RF components, and particularly to RF Power resistors.
2. Technical Background
In one approach that has been considered, a conventional RF power resistor 100 is shown in FIG. 10. Resistor 100 includes: a substrate material 102; conductive traces 104; and a resistive structure 106. The substrate material is typically fired and lapped ceramic, with BeO, AlN (aluminum nitride) or Alumina being typical substrate materials. Secondary processing includes making holes and slots, typically drilled by a laser as needed. The conductive traces and pads are typically made of silver (Ag) (printed Ag paste).
In resistor 100, resistive structure 106 is typically made from a resistive paste that is made of a mixture of materials as is known in the prior art (as is printed on the ceramic substrate 102). The resistive structure is a single layer structure. It is not a transmission line as it is typically much wider (in a direction transverse to current flow) than the impedance desired on the input port, hence transmission line is used for matching the relatively wide resistor to the desired impedance. Herein, this type of resistor will be called a “widepath resistor” or a “widepath structure” in order to distinguish this kind of structure from a transmission line structure.
Because of the geometry and/or material used to make widepath resistor 106, the widepath resistor itself must be tuned, which is costly and labor intensive. Some other recognized performance limitations of conventional widepath resistors are as follows:
(i) maximum temperature limit between 200 C to 250 C;
(ii) performance drift when operated at or above 200 C for extended duration;
(iii) hard failure if operated above 250 C;
(iv) as resistor footprint increases to become greater than 0.5 by 0.5 inches the risk of cracking drastically increases; and (v) Labor intensive manufacturing process (for example, must generally tune each resistor individually);
With respect to issue (iv) listed above, the cracking risk is due to coefficients of thermal expansion (“CTE”) mismatch between the ceramic substrate and the widepath resistor structure, and it is believed to be an exponentially increasing cracking risk as footprint area increases. Historically, 50% yields have been observed for 1.0 square inch square resistors of the type corresponding to resistor 100.
By way of background, a “delay line” (which is not considered to be an RF power resistor or analogous to an RF power resistor) is a non-resistor device that is used to control the timing of an RF signal. While a delay line device will generally attenuate the input signal a certain amount, delay lines are designed to minimize attenuation and are configured to act as little like resistors as possible. A delay line device includes a long transmission line structure (not a widepath structure) which includes: (i) a highly conductive layer, with traces; and (ii) a dielectric material layer. The highly conductive material is typically copper and the dielectric material is typically made of circuit board material. Because the highly conductive material is highly conductive, the use of the delay line will not generate much heat which is why simple circuit board material (as opposed to ceramic or the like) can be used for the dielectric layer.
The following published document(s) (which may or may not legally constitute prior art) may also include helpful background information: US patent application 2008/0258838 ('838 Oshima”).
Technical Background Section Disclaimer: To the extent that specific publications are discussed above in this Technical Background Section, these discussions should not be taken as an admission that the discussed publications (for example, published patents/patent applications) are prior art for patent law purposes. For example, some or all of the discussed publications may not be sufficiently early in time, may not reflect subject matter developed early enough in time and/or may not be sufficiently enabling so as to amount to prior art for patent law purposes. To the extent that specific publications are discussed above in this Technical Background Section, they are all hereby incorporated by reference into this document in their respective entirety(ies).